In recent years, orthogonal dual-polarized antennas and orthogonal dual-polarized antenna arrays in which multi-input-multi-output (MIMO) communications can be achieved by polarization diversity have been in practical use, for example, as base stations for mobile communications or antenna apparatuses for Wi-Fi communication devices to ensure communication capacity. Most of the orthogonal dual-polarized antennas and the orthogonal dual-polarized antenna arrays are composed of two antenna elements that are arranged to be substantially vertical to each other and an array of the antenna elements. In order to prevent a decrease in the communication capacity, it is required to suppress the coupling between the two antenna elements. While the coupling between the two antenna elements can be suppressed by separating the two antenna elements, it is also required to increase the integration degree of the antenna elements and to reduce the size of the antenna in order to reduce the size of the whole apparatus.
Antennas disclosed in Patent Literature 1, 2, and 3 are examples of the above orthogonal dual-polarized antenna. These antennas have a structure in which two antenna elements (in these examples, dipole antennas) are arranged in a cross shape so that the centers of the respective antenna elements overlap and become orthogonal to each other, whereby it is possible to reduce the size of the whole antenna while suppressing the coupling between the two antenna elements.